A 3D Homochiral MOF [Cd2(d-cam)3]?2Hdma?4dma for HPLC Chromatographic Enantioseparation

Article abstract of DOI:10.1002/chir.22588

Up to now, some chiral metal-organic frameworks (MOFs) have been reported for enantioseparation in liquid chromatography. Here we report a homochiral MOF, [Cd2(d-cam)3]·2Hdma·4dma, used as a new chiral stationary phase for high-performance liquid chromatographic enantioseparation. Nine racemates of alcohol, naphthol, ketone, and base compounds were used as analytes for evaluating the separation properties of the chiral MOF packed column. Moreover, some effects such as mobile phase composition, column temperature, and analytes mass for separations on this chiral column also were investigated. The relative standard deviations for the resolution values of run-to-run and column-to-column were less than 2.1% and 3.2%, respectively. The experimental results indicate that the homochiral MOF offered good recognition ability, which promotes the application of chiral MOFs use as stationary phase for enantioseparation. Chirality 28:340-346, 2016.

Full text of DOI:10.1002/chir.22588

CHIRALITY 28:340–346 (2016)
A 3D Homochiral MOF [Cd (d-cam) ]•2Hdma•4dma for HPLC
2
3
Chromatographic Enantioseparation
MEI ZHANG, XINGLIAN CHEN, JUNHUI ZHANG, JIAO KONG, AND LIMING YUAN *
1
2
3
4
4
1
Department of Traditional Chinese Medicine, Yunnan University of Traditional Chinese Medicine, Kunming, P. R. China
2
Agricultural Science Research Institute of Quality Standards and Testing Technology Institute of Yunnan Province, Kunming, P. R. China
3
Department of Chemistry, East China Normal University, Shanghai, P. R. China
4
Department of Chemistry, Yunnan Normal University, Kunming, P. R. China
ABSTRACT
for enantioseparation in liquid chromatography. Here we report a homochiral MOF,
Cd2(d-cam)3]·2Hdma·4dma, used as a new chiral stationary phase for high-performance liquid
Up to now, some chiral metal-organic frameworks (MOFs) have been reported
[
chromatographic enantioseparation. Nine racemates of alcohol, naphthol, ketone, and base
compounds were used as analytes for evaluating the separation properties of the chiral MOF
packed column. Moreover, some effects such as mobile phase composition, column tempera-
ture, and analytes mass for separations on this chiral column also were investigated. The relative
standard deviations for the resolution values of run-to-run and column-to-column were less than
2
.1% and 3.2%, respectively. The experimental results indicate that the homochiral MOF offered
good recognition ability, which promotes the application of chiral MOFs use as stationary phase
for enantioseparation. Chirality 28:340–346, 2016. © 2016 Wiley Periodicals, Inc.
KEY WORDS: metal-organic frameworks; chiral stationary phase; high-performance liquid
chromatography; racemates; enantioseparation
Taking into account the importance of chiral recognition,
tremendous research effort has been devoted to research and
develop chiral recognition materials. As a new functional
material, metal-organic frameworks (MOFs) are one type of
novel crystalline material constructed from clusters of metal
the potential enantioselectivity of MOFs and optimizing the
separation efficiency.
Templated by organic cation and chiral anion, a 3D homochi-
ral porous MOF [Cd (d-cam) ]·2Hdma·4dma (1) (d-H cam =
2
3
2
d-camphoric acid, dma = dimethylamine ) exhibits an unprece-
dented six-connected net. The free space in this six-connected
net is larger than that in the eight-connected body-centered
cubic (bcu) net (see Supplementary Material Fig. S1), which
can provide the adequate surface area required for solute reten-
tion (impact on resolution). Its unique structures, high surface
area, and excellent chemical stability make 1 promising in
enantioseparation. Herein, we present 1 as a new chiral station-
ary phase for HPLC enantiomeric separation of various chiral
compounds with good selectivity especially for (±)-
1-(1-naphthyl)ethanol, which indicates that the enantioseparation
on this chiral MOF column is practical in HPLC.
1
ions or cluster nodes and organic linkers. The current interest
in MOFs is rapidly expanding, not only for their fascinating
2
-4
architectures and intriguing topologies, but also for potential
5
-10
11-15
applications in gas storage,
separation,
heterogeneous
catalysis,1 and many other areas.
6-18
19-22
As a suitable chromato-
graphic separation media, MOFs have been employed as
stationary phases for high-performance liquid chromatography
3-29
30-33
(
HPLC),2
high-resolution gas chromatography (GC),
3
4,35
and capillary electrochromatography (CEC),
and the re-
sults demonstrated remarkable success in separating mixtures
of compounds in small volumes.
Up to now, the synthesis of homochiral metal-organic frame-
works has attracted much attention due to their wide application
in asymmetric catalysts and enantioselective separations.36 The
incorporation of enantiomerically pure homochiral building
blocks into microporous materials creates potential opportuni-
MATERIALS AND METHODS
Materials
All chemicals were at least of analytical grade. Ultrapure water (18.2 MΩ
cm) was obtained with an ELGA LabWater water purification system (UK).
Hexane, dichloromethane (DCM), isopropanol, and N,N-dimethylformamide
(DMF) were from Tianjin Guangfu Fine Chemical Research Institute (Tian-
37
ties for separation of enantiomers. Among so many reported
3
8-45
homochiral MOFs, a lot of them have been studied for GC,
46-48
49-57
CEC,
CSPs). The first example in liquid chromatography was that a
enantiopure [Zn (bdc)(L-lac)(dmf)]·DMF was used for the
and HPLC
for use as chiral stationary phases
3 2 2
jin, China). Cadmium nitrate tetrahydrate (Cd(NO ) ·4H O, 99%), (S)-(+)-
2
-methylpiperazine (98%), and D-(+)-camphoric acid (d–cam, 99%) were
(
purchased from Adamas (Emeryville, CA), while ethanol (HPLC grade)
was from Tedia (Fairfield, OH). For the nine racemates and their correspond-
ing enantiomers, 1-(4-chlorophenyl)ethanol were from Alfa Aesar (Ward Hill,
MA), 1-(9-Anthryl)-2,2,2-trifluoroethanol, 1,1’-bi-2-naphthol, benzoin,
2
49
separation of chiral alkyl aryl sulfoxides, then chiral MOF
Bn-ChirUMCM-1 was applied for 1-phenylethanol separation
50
with low resolution and selectivity, and the (R)-MOF-silica
composite is also only used for chiral sulfoxides separation,51
all of them showing a narrow range of chiral enantioselectivity.
Then several chiral MOFs were used for CSP by our group.5
Since the promising application of chiral MOFs for
enantioseparation in HPLC, it is necessary to further explore
*
Correspondence to: Li-Ming Yuan, Department of Chemistry, Yunnan Normal
University, Kunming 650500, P.R. China. E-mail: yuan_limingpd@126.com
Received for publication 30 November 2015; Accepted 29 January 2016
DOI: 10.1002/chir.22588
2-55
Published online 22 February 2016 in Wiley Online Library
(wileyonlinelibrary.com).
©
2016 Wiley Periodicals, Inc.

3D HOMOCHIRAL MOF
341
hydrobenzoin, and trans-stilbene oxide were obtained from Acros (Somer-
ville, NJ), 1-(1-naphthyl)ethanol from Fluka (Buchs, Switzerland),
praziquantel from Sigma (St. Louis, MO), and warfarin sodium from TCI
RESULTS AND DISCUSSION
Characterization of Synthesized 1
The powder X-ray diffraction (PXRD) pattern of the synthe-
sized 1 (see Supplementary Material Figure S2b) was in good
agreement with the simulated one (see Supplementary
(Portland, OR).
Instrumentation
The powder X-ray diffraction (PXRD) patterns were obtained with a
58
Material Figure S2a) and the results of Zhang et al., which
confirmed the successful synthesis of 1. In order to release
more free spaces within the framework, the colorless solid
was heated at 100ꢀC in vacuo for 6 h to form dehydrated 1.
Fortunately, both the thermal gravimetric analysis (TGA) of
D/max-3B diffractometer (Rigaku, Japan) using Cuka radiation. The scanning
electron microscopy (SEM) images were recorded on a Hitachi S-3000N
scanning electron microscope (Japan) at 15.0 kV. The TGA experiment was
performed on a ZRY-1P Simultaneous Thermal Analyzer (Shanghai, China).
The stainless steel empty column (250 mm long × 2.1 mm i.d.) and 1/3
HP liquid pump were purchased from Alltech (Deerfield, IL). All HPLC
separations were performed on a chromatographic system consisting of
a Shimadzu LC-15C HPLC pump and a SPD-15C UV-vis detector. The
Auto Science AT-330 column heater (±0.1ꢀC) was used to control the
column temperature during HPLC separation. The data acquisitions were
carried out with N-2000 software
1
before and after samples activation (see Supplementary Ma-
terial Figure S3) and the PXRD pattern of the evacuated solids
(see Supplementary Material Figure S2c) is similar to that of
the pristine solids, which have demonstrated that 1 can be
activated without breaking the open structure before being
used as the chiral stationary phase for the HPLC column.
In order to get small particles and a narrow particle size dis-
tribution, the activating 1 was crushed in ethanol, applying
soft pressure. With the help of solvent suspension, the SEM
image exhibited the crystals of 1 with an average size of 5
μm (see Supplementary Material Figure S4).
Synthesis and Characterization of Crystal 1
1
was synthesized solvothermally by employing mixed organic solvents
58
according to the method of Zhang et al. Typically, Cd(NO
3
)
2
·4H
0.1501 g), (S)-(+)-2-methylpiperazine (0.0263 g), and D-Camphoric acid
0.1050 g) were dissolved in a solvent mixture of DMF (1.8366 g) and
OH (0.9524 g), then the sample was sealed in a 23-mL Teflon cup
2
O
(
(
HPLC Enantioseparation on Cd-MOF Column
2 5
C H
and heated at 100ꢀC for 10 d. After cooling down, the resultant colorless
crystals were washed thoroughly with ethanol and distilled water. The
yield was 86%.
It is one of the most compelling challenges to separate chiral
compounds because of their similar physical and chemical prop-
erties. Here we first tested the 1 packed column for the various
important racemates separation to investigate the chiral recogni-
tion ability of this stationary phase. Fortunately, the following
nine racemates were well separated on the Cd-MOF column:
1-(1-naphthyl)ethanol, 1-(4-chlorophenyl)ethanol, 1-(9-anthryl)-
2,2,2-trifluoroethanol, 1,1’-bi-2-naphthol, benzoin, hydrobenzoin,
trans-stilbene oxide, praziquantel, and warfarin sodium. The cor-
Column Packing Procedure for HPLC Measurement
In order to control the packing quality, a conventional high-pressure
slurry packing procedure was adopted. A 1.50 g mass of prepared 1 was
dispersed in a vessel with 25 mL of DCM and then packed into a stainless
steel empty column (25 cm long × 2.0 mm i.d.) under 40 MPa with
hexane/DCM (9:1, v/v) as the slurry solvent, and the crystals could
disperse slowly by changing the pressure to press the slurry into the
responding mobile phase, retention factors (k ’) for the first
1
eluted enantiomer, separation factors (α), and resolution (RS)
on Cd-MOF column for the separated racemates are listed in
Table 1. As can be seen, the chiral Cd-MOF column gave high
2 3
column, then a better [Cd (d-cam) ]·2Hdma·4dma packing column
(Cd-MOF column) was obtained. The Cd-MOF column was equilibrated
with hexane/DCM (9:l, v/v) until the baseline stabilized before the
chromatographic experiments.
resolution for 1-(1-naphthyl)ethanol (R =4.55) and baseline sep-
S
aration of 1,1’-bi-2-naphthol and 1-(4-chlorophenyl)ethanol with
good peak chromatograms; meanwhile benzoin, 1-(9-Anthryl)-
Calculation of the Chromatographic and Thermodynamic
Parameters
The retention factors (k′), separation factors (α), and resolution values
2
,2,2-trifluoroethanol, and trans-stilbene oxide showed a signifi-
cant overlap of the peaks because of their strong tailing. Six
corresponding enantioseparation chromatograms are shown in
Figure 1. It is possible that the peaks tailing arise from the stron-
ger interaction of the chiral selector by hydrogen bonding
because most of the analytes are chiral aromatic alcohol. For
further optimization of the separation efficiency, a larger column
adapted or a gradient elution is necessary.
S
(R ) were calculated from Equations (1), (2), and (3), respectively.
k1′ ¼ ðt1 ꢀ tM Þ=tM
(1)
(2)
α ¼ ðt2 ꢀ tM Þ=ðt1 ꢀ tM Þ
ꢀ
ꢁ
RS ¼ 1:18ðt2 ꢀ t1Þ= W1=2 þ W1=2ð1Þ
(3)
ð2Þ
where t
M
is the column void time, which was determined by 1,3,5-tri-
TABLE 1. Separations of racemates on Cd-MOF column
tert-butyl- benzene, t
and t for the slower, and W1/2(1) and W1/2(2) are the corresponding peak
widths at half height.The temperature dependence of the retention factor
1
is the retention time for the faster-moving analytes
2
Racemates
Mobile phase (v/v)
k ’
1
α
Rs
59
k′ can be described by the van’t Hoff equation, (Eq. 4). Their Gibbs free
energy change (ΔG) calculated using Equation (5).
1-(1-naphthyl)ethanol
1-(4-
hexane/DCM (1:1) 1.26 5.70 4.55
hexane/DCM (1:1) 1.04 2.82 1.26
chlorophenyl)ethanol
ΔH ΔS
1
-(9-anthryl)-2,2,2-
trifluoroethanol
,1’-bi-2-naphthol
hexane/DCM (4:1) 1.40 1.30 0.52
lnk′ ¼ ꢀ RT
þ
þ lnΦ
(4)
R
1
hexane/DCM (2:1) 0.68 2.24 1.76
hexane/DCM (1:1) 1.06 1.40 0.62
hexane/DCM (4:1) 1.49 1.28 0.42
hexane/DCM (1:2) 1.32 1.38 0.59
hexane/DCM (2:3) 1.50 1.27 0.46
hexane/DCM (1:2) 0.31 5.40 0.54
benzoin
ΔG ¼ ΔH ꢀ TΔS
(5)
hydrobenzoin
trans-stilbene oxide
praziquantel
Here ΔH is the enthalpy change and ΔS is the entropy change for the
transfer of solutes from the mobile phase to the stationary phase, T is
the absolute temperature, R is the gas constant, and Φ represents the
column phase ratio.
warfarin sodium
Chirality DOI 10.1002/chir

3
42
ZHANG ET AL.
Fig. 1. HPLC chromatograms on the packed Cd-MOF column` (25 cm long × 2.1 mm i.d.) for the separation of racemates. (A) 1-(1-naphthyl)ethanol, (B) 1,1’-bi-2-
naphthol, (C) 1-(4-chlorophenyl)ethanol, (D) benzoin, (E) 1-(9-anthryl)-2,2,2-trifluoroethanol, and (F) trans-stilbene oxide at 25ꢀC using different ratio of hexane/
DCM as the mobile phase at a flow rate of 0.1 mL min-1. The signals were monitored with a UV detector at 254 nm.
Cd-MOF Column Compared With Three Commercial Chiral
Columns
column manually to separate the three relevant racemates
(see Supplementary Material Table S1). The corresponding
separation factors are listed in Table S2 (see Supplementary
Material). The results showed that 1-(1-naphthyl)ethanol
failed to separate on the three commercial chiral columns
but obtained good separation on [Cd (d-cam) ]·2Hdma·4dma
In order to compare chiral MOF [Cd (d-cam) ]·2Hdma·
2
3
4
1
dma CSP with other chiral CSPs for enantioseparation of
-(1-naphthyl)ethanol, 1,1’-bi-2-naphthol, and 1-(4-
2
3
chlorophenyl)ethanol, three commercial chiral columns
Chiralpak AD, Chiralpak IA, and (S, S)-Whelk-01) were
employed at the recommended optimal mobile phase in each
CSP. In addition, this new chiral MOF CSP gave higher reso-
lution for 1,1’-bi-2-naphthol and 1-(4-chlorophenyl)ethanol
than that of the three commercial chiral CSPs. The results
(
Fig. 2. Effect of the mobile phase composition on the HPLC separation on Cd-MOF column (25 cm long × 2.1 mm i.d.) at a flow rate of 0.1 mL min-1 at 25ꢀC. (A)
-(1-naphthyl)ethanol; (B) 1-(4- chlorophenyl)ethanol; (C) 1,1’-bi-2-naphthol; (D) 1-(9-anthryl)-2,2,2-trifluoroethanol. The signals were monitored with a UV detector
1
at 254 nm.
Chirality DOI 10.1002/chir

3D HOMOCHIRAL MOF
343
indicated that [Cd (d-cam) ]·2Hdma·4dma CSP offered a
2
3
good chiral recognition ability, especially for aryl alcohols.
Effect of Different Composition of the Mobile Phase on
Cd-MOF Column
As all we know, the composition of the mobile phase plays a
significant role in retention, selectivity, and resolution in HPLC
separation studies. Here we took 1-(1-naphthyl)ethanol, 1-(4-
chlorophenyl)ethanol, 1,1’-bi-2-naphthol, and 1-(9-anthryl)-
2
,2,2-trifluoroethanol as examples to investigate the effect of
the mobile phase on the Cd-MOF column. The results showed
that the mobile phase composition affected both the retention
and the resolution of racemates on the Cd-MOF column to
some extent (Fig. 2). As the content of DCM increased in the
mobile phase, although the shape of peaks were improved, both
the retention time and the separation efficiency of 1-(1-
naphthyl)ethanol, 1,1’-bi-2-naphthol, and 1-(9-anthryl)-2,2,2-
trifluoroethanol decreased. However, only a slight change in
the retention time and selectivity for 1-(4-chlorophenyl)ethanol
was seen when the ratio of DCM-hexane increased more than
Fig. 4. Van’ t Hoff plots for the separation of (1-naphthyl)ethanol on the
Cd-MOF column with hexane/DCM (1/1) as the mobile phase at a flow rate
of 0.1 mL min-1.
1
/2 even up to pure DCM (Fig. 2B). In contrast to the binary
retention time of S(–)-1-(1-naphthyl)ethanol on the Cd-MOF col-
umn was gradually reduced while little changed for R(+)-
hexane/DCM, the hexane/isopropanol system gave poor reso-
lution for 1-(1-naphthyl)ethanol (Fig. 2A). What’s more, al-
though with similar polarity, 1-(1-naphthyl)ethanol could
obtain outstanding separation by hexane/DCM (1/1), while it
failed to get separated under hexane/isopropanol (3/2), which
can be seen clearly in Figure 2A. The most probable reason
was that most of the analytic racemates had weak hydrogen-
bond forces on MOF with alcohols, as the competition from al-
1
1
-(1-naphthyl)ethanol, that is to say, the selectivity of (±)-
-(1-naphthyl)ethanol slightly decreased when the column
temperature increased (Fig. 3). The van’t Hoff plots suggested
no changes in the interaction mechanism in relation to tempera-
ture for the separation of (±)-1-(1-naphthyl)ethanol in the studied
temperature range since it showed good linearity (Fig. 4). Table 2
gives the values of enthalpy change (ΔH) and entropy change
(ΔS) obtained from the van’t Hoff plots of Equation (4), and those
of the Gibbs free energy change (ΔG) calculated using Equation
cohol solvent adsorption was decreased when compared to
DCM.59 In the hexane–isopropanol system, Cd-MOF may ad-
sorb 1-(1-naphthyl) ethanol mainly via dipole–dipole forces; in
contrast, hydrogen-bonding forces lead 1-(1-naphthyl) ethanol
adsorption in a hexane–DCM mobile phase. Since the
Cd-MOF has hydrogen-bonding forces with isopropanol, the
enantioselectivity is decreased by the competition from alcohol
solvent adsorption when compared to DCM.
(5). The negative values of ΔG indicate that the transfer of 1-(1-
naphthyl)ethanol from the mobile phase to the stationary phase
of 1 was a thermodynamically spontaneous process, and this
process was controlled by negative ΔH and ΔS. As can be seen
from Table 2, S(–)-1-(1-naphthyl)ethanol gave more negative
ΔG in comparison with R(+)-1-(1-naphthyl)ethanol, thereby
showing a stronger retention on the stationary phase 1.
Influence of Temperature for Enantioseparation on
Cd-MOF Column
Different Mass of 1-(1-naphthyl)ethanol for Separation on
Cd-MOF Column
To gain further insight into the influence of the
enantioseparation on the Cd-MOF column, 1-(1-naphthyl)ethanol
was taken as an example to separate at temperatures from 20 to
To the best of our knowledge, there has been no attempt to
utilize chiral MOFs as stationary phases for enantioseparation
of (±)-1-(1-naphthyl)ethanol in HPLC with excellent resolu-
35ꢀC because of its outstanding resolution and selectivity. The
tion (R =4.55). To gain further insight into the separation of
S
1
for separation of (±)-1-(1-naphthyl)ethanol, different masses
of 1-(1-naphthyl)ethanol in hexane/DCM (1/1) were injected
into the Cd-MOF column for separation. As can been seen
from Figure 5, the retention time and the selectivity for the
analyte slightly decreased but also offered baseline separa-
tion when the mass of sample increased, which indicates that
crystal 1 is favorable for its application in the analytical sepa-
ration of 1-(1-Naphthyl)ethanol.
Stability and Reproducibility of Cd-MOF Column
After HPLC measurement, the column material’s PXRD
pattern (see Supplementary Material Fig. S2d) was coincident
to the activating solids before use (see Supplementary Mate-
rial Fig. S2c), which proved that the structure of crystals of
1
did not change when used as the chiral stationary phase
Fig. 3. Chromatograms on the Cd-MOF column for the separation of 1-(1-
for enantioseparation in HPLC. The repeatability of the
Cd-MOF column was determined following five repeated
Chirality DOI 10.1002/chir
naphthyl)ethanol at 20 to 35ꢀC using hexane/DCM (1/1) as the mobile phase
at a flow rate of 0.1 mL min-1 with UV detection at 254 nm.

3
44
ZHANG ET AL.
2
TABLE 2. Values of ΔH, ΔS, ΔG (25°C), and γ
-1
-1 -1
ꢀ1
2
Enantiomers
ΔH (kJ mol )
ΔS (J mol k )
ΔG (kJ mol
)
γ
R(+)-1-(1-naphthyl)ethanol
S(-)-1-(1-naphthyl)ethanol
-17.82 ± 0.93
-26.77 ± 0.69
-41.18 ± 3.08
-56.57 ± 0.28
-5.55 ± 0.93
-9.91 ± 0.69
0.984
0.996
a
γ refers to the linear correlation coefficient of ln k’-1/T plot for the HPLC separation of (±)-1-(1-naphthyl)ethanol on a column packed with 1 and using hexane/
-
1
DCM (1/1) as the mobile phase at a flow rate of 0.1 mL min .
2
D intersecting channels along the a and b axes (see Supple-
mentary Material Figure S6, which shows the cylindrical
channels along the a axis). According to the PLATON pro-
3
gram, the solvent-accessible volume is ~1462.3 Å per unit
cell, and the pore volume ratio was calculated to be 33.4%.58
Consequently, the separation of racemates mostly depends
on the pore size, shape of the channel, and host–guest inter-
action effects of the stationary phase.60 In addition, many
other interactions such as hydrogen, dipole–dipole, disper-
sion force, and so on that come from 1 and the mobile phase
may also affect the enantioselectivity.
CONCLUSION
In conclusion, we have reported that a homochiral MOF
possesses excellent chiral recognition ability for some aryl al-
cohols enantiomers in HPLC. Particularly, columns packed
with 1 are very attractive for specific recognition and separa-
tion of (±)-1-(1-naphthyl)ethanol for its outstanding resolution
values. The results show that 1 explored as a novel chiral sta-
tionary phase for HPLC enantioseparation is practicable, and
this work may bring a bright future for chiral MOFs in the
specific separation of some racemates.
Fig. 5. HPLC chromatograms of 1-(1-naphthyl)ethanol with different
injected masses at 25ꢀC using hexane/DCM (1/1) as the mobile phase at a
flow rate of 0.1 mL min-1 with UV detection at 254 nm.
injections of (±)-1-(1-naphthyl)ethanol (Fig. 6); the RSDs for
RS were 2.1% (interday, n = 5), which indicated good stability
of the Cd-MOF column. Then the column-to-column RSDs
ACKNOWLEDGMENTS
(
n = 3) were 3.2% for the separation of 1,1’-bi-2-naphthol,
We thank Prof. Jian Zhang, Dr. Jia Jia, and Miss Ying-juan
Peng for their help in the X-ray data analysis. This work was
supported by the National Nature Science Foundation (No.
which confirmed the good reproducibility of the column
preparation.
2
1275126, No. 21127012) and Key Project of Science Founda-
Possibility Chiral Recognition Mechanism
tion by the Department of Education, Yunnan Province,
China (Grant No. 2015Z122).
The excellent chiral recognition ability of the 1 packed
Cd-MOF column was mainly dependent on the well-defined
coordination geometries of the metal centers where the
ordered d-cam ligands connect the dinuclear Cd units into
wavelike (4,4) sheets (see Supplementary Material Fig. S5)
and the 3D homochiral open framework of 1 contains large
SUPPORTING INFORMATION
Additional supporting information may be found in the
online version of this article at the publisher’s web-site.
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